Field of the Invention
The present invention relates to a combustion system, and more particularly to a fuel supply/ignition device and an internal combustion engine utilizing this device.
Various systems of stratified combustion have been proposed such that a rich fuel mixture layer and a lean fuel mixture layer are formed in a cylinder of the internal combustion engine, and a flame generated by igniting the rich fuel mixture layer is propagated to the lean fuel mixture layer to burn a generally lean fuel mixture.
An example of the internal combustion engine achieving such a stratified combustion system is known as a so-called MAN-FM engine. The MAN-FM engine is described in SAE 820760 and SAE 690255 which are well-known technical literatures in automotive and internal combustion engine fields.
FIG. 18 shows an essential part of the MAN-FM engine. Referring to FIG. 18, a combustion chamber 710 formed at a central portion of a piston head 702 of a piston 700. The combustion chamber 710 has a nearly spherical shape. A fuel injection nozzle 720 and a spark plug 730 are so provided as to be directed into the combustion chamber 710. Air is induced into the combustion chamber 710 so as to generate a swirl as shown by an arrow X, and fuel is injected from the fuel injection nozzle 720 toward an inner wall surface 715 of the combustion chamber 710. The swirl of the induced air in the combustion chamber 710 serves to form a radially stratified fuel mixture. The spark plug 730 generates a spark for a long discharge time and applies the same to an optimum fuel mixture layer to be formed at an area near the inner wall surface 715 of the combustion chamber 710, thus carrying out ignition. The combustion is contorolled according to a speed of formation of the fuel mixture by the swirl and vaporization of the fuel from the inner wall surface 715 of the combustion chamber 710.
In the fuel supply/ignition device achieving the stratified combustion in the conventional internal combustion engine, the violent swirl generated in the combustion chamber 710 fluctuates a fuel-air ratio of the fuel mixture reaching the spark plug 730. Accordingly, a proper fuel-air ratio cannot be always obtained at an ignition timing to cause unstable ignitability such as ignition failure. Furthermore, as the fuel is injected toward the inner wall surface 715 of the spherical combustion chamber 710, and is expanded along the inner wall surface 715 by the swirl, a fuel film is disadvantageously formed to cause the generation of an unburnt gas. As a result, there occurs another problem of increase in HC in an exhaust gas. Furthermore, as the fuel is injected under a high pressure from the fuel injection nozzle 720 toward the inner wall surface 715 of the combustion chamber 710, a large part of the fuel is deposited onto the inner wall surface 715 to cause deterioration in fuel atomization.